On Sunday 6th September 2011 I finally got around to putting the crankshaft back into the cases.
By looking at where the locator dowels on the two crankcase halves are, it is quite easy to work out which bolts go where when reassembling the crankcase halves. The engine had been apart for so long that I had long since forgotten pulling it apart.
I did come across a few tricky bits that I was not too sure of:
1) The stepped collar for the gear change pawl moving arm
2) The washer for the water pump drive. The plastic gear did have some nasty looking cracks in it where it meets the steel shaft. This is not good. However, I have just ignored this for now. Hmmmm.
3) The washer for the gear shift shaft
4) The washer for the oil pump.
.
5) Also, I forgot the locator dowel for the cassette gearbox mounting plate the first time I assembled it. And as I was tightening it into place, it felt like something was wrong. I soon realised that I needed to flick the tail of the gear pawl spring up into place as I was sandwiching it between 2 aluminium faces.
.
6) There is also a washer on the kickstart shaft, but this I already had twist-tied to the shaft.
.
7) One thing that seems to escape mention in diagrams and manuals etc is the small sub-assembly that looks like some sort of idler gear that bolts on across the two crankcase halves via three 5mm Allen Head cap screws. I believe this is just a simple little oil pump that pumps oil from the outer (clutch side) of the gearbox case and sprays the oil onto the gearbox shafts on the inside part of the gearbox, helping to keep the gears well lubricated. Even the NSR-World website incorrectly refers to this as the "Oil/Water pump drive gear". (Fourth to bottom picture here).
The two little dowels and the two O-rings that go behind this Gearbox Oil Pump/Sprayer Gear sub-assembly are perhaps not all that obvious, so I thought I would just mention them here for completeness.
[edit] Actually, after thinking about this a bit, I have come to realise that I don't actually know what this thing does. But my above explanation is probably wrong. [/edit]
Just to prove my point here, I will show the photo below. Clearly the white nylon helically cut Water/Oil pump drive gear is driven by the helically cut primary crankshaft gear (along with the helically cut clutch ring gear) and NOT by this straight cut Gearbox oil pump/sprayer gear.
8) I was unable to get a replacement oil seal for the dry clutch. The MC18 has a main dry clutch oil seal with ID 68mm, OD 84mm, and width 8mm. The MC21 has a different sized oil seal: ID 69mm, OD 84mm, and width 8mm. So I had no choice but to re-use the old seal, which still seemed to be in quite good condition.
9) One thing that I unfortunately could not do, was line up the red dot on the primary crank gear with the associated mark on the end of the crankshaft. I did mark it with a marker pen on dis-assembly, but the marking has worn off over time somehow. I am not at all sure how critical this is. I guess it is an engine balance thing. I imagine that the primary gear is fairly well balanced due to its symmetry. I hope! I guess if the motor vibrates a lot, this may be a reason why? I am hoping it will not matter. Fingers crossed.
By looking at where the locator dowels on the two crankcase halves are, it is quite easy to work out which bolts go where when reassembling the crankcase halves. The engine had been apart for so long that I had long since forgotten pulling it apart.
I did come across a few tricky bits that I was not too sure of:
1) The stepped collar for the gear change pawl moving arm
 |
| Stepped collar sits on pin and fits into gear change slot |
2) The washer for the water pump drive. The plastic gear did have some nasty looking cracks in it where it meets the steel shaft. This is not good. However, I have just ignored this for now. Hmmmm.
 |
| Nasty looking cracks |
 |
| Left washer is for oil pump, centre washer is for water pump, right washer is for gear change shaft below |
3) The washer for the gear shift shaft
 |
| Washer goes on after circlip |
4) The washer for the oil pump.
.
5) Also, I forgot the locator dowel for the cassette gearbox mounting plate the first time I assembled it. And as I was tightening it into place, it felt like something was wrong. I soon realised that I needed to flick the tail of the gear pawl spring up into place as I was sandwiching it between 2 aluminium faces.
 |
| Cassette gearbox locator dowel (Dia. 8.00mm x 17.9mm) |
 |
| Gear change spring needs to be flicked up |
 |
| Gear change spring flicked up |
6) There is also a washer on the kickstart shaft, but this I already had twist-tied to the shaft.
.
7) One thing that seems to escape mention in diagrams and manuals etc is the small sub-assembly that looks like some sort of idler gear that bolts on across the two crankcase halves via three 5mm Allen Head cap screws. I believe this is just a simple little oil pump that pumps oil from the outer (clutch side) of the gearbox case and sprays the oil onto the gearbox shafts on the inside part of the gearbox, helping to keep the gears well lubricated. Even the NSR-World website incorrectly refers to this as the "Oil/Water pump drive gear". (Fourth to bottom picture here).
The two little dowels and the two O-rings that go behind this Gearbox Oil Pump/Sprayer Gear sub-assembly are perhaps not all that obvious, so I thought I would just mention them here for completeness.
[edit] Actually, after thinking about this a bit, I have come to realise that I don't actually know what this thing does. But my above explanation is probably wrong. [/edit]
 |
| What does this thing do? Does it pump oil from A to B? |
OK, after thinking about this a bit more, it seems likely that it pumps oil through little oil ways to the (inside of the ??) counter shaft and drive shaft. But I still don't know for sure. I need to pull my old engine apart some more and study where the oil-ways actually go.
[Edit 2016-05-17 I sussed out the transmission oil pump pathway and posted about it at over at NSR250.FreeForums.org ]8) I was unable to get a replacement oil seal for the dry clutch. The MC18 has a main dry clutch oil seal with ID 68mm, OD 84mm, and width 8mm. The MC21 has a different sized oil seal: ID 69mm, OD 84mm, and width 8mm. So I had no choice but to re-use the old seal, which still seemed to be in quite good condition.
 |
| MC18 Dry Clutch seal is 68mm ID NOT 69mm ID like MC21 |
.
Other than the above things, it is all pretty obvious stuff I think.
Actually, I did come across one other little point of interest. I found a parts list (in Japanese) for the MC21 online and downloaded it. It showed that the inner-most steel clutch plate had a different part number to the rest of the steel clutch plates. Also, the inner-most fibre clutch plate had a different part number than the rest of the fibre clutch plates.
I soon realised that one of my fibre clutch plates was indeed different to the rest as it had slots cut into four of the castellated engagement tabs to take anti-vibration rubbers. However, all 6 of the steel plates appeared to be similar. I double checked this on a spare MC18-SP engine that I have, and I found that one of the steel clutch plates was different. Most of the steel plates measure 2.89 - 2.94mm thick with my digital verniers. But there is a different steel plate that has a slightly concave shape that is made out of 2.0 mm thick steel. It measures about 3mm thick along the axis of the clutch due to its concave shape.
The different plates are the inner-most plates, The steel one sits so that the small diameter side of it goes on the inside. I went over the steel plates with some 240 grit wet-n-dry sandpaper just to "de-glaze" them a bit.
.
I am currently trying to get some Wossner RM125 pistons. These are single ring pistons with about a 5mm shorter skirt than the standard NSR250 pistons. When/if I get them, I will be machining the heads slightly to get a good squish and even combustion volumes on both cylinders.
Well, my "A" barrels measured up to be 54.02mm diameter at the top and 54.01mm at the bottom.
So I will be getting pistons made to be 53.96mm max diameter so as to give 0.05mm clearance at the tightest diameter of the cylinder bore (being 54.01 the bottom at the bottom less 0.05mm)
Basically this is the 0.01 oversize 2000-2003 RM125 piston from Wossner. (Part Number 8061DB)
Wossner also do a NSR125 piston at 53.96. But I want to go nuts and get the (assumedly lighter) RM piston as it has a 5mm shorter skirt and a single ring.
.
[Edit] My man getting the Wossner pistons spoke to "Luigi" at Wossner in Germany. Luigi suggested going with a clearance of 0.05mm at the 54.02 diameter top of the bore. So the pistons will be 53.97mm nominal diameter. This change is very minor, but the piston is hottest (and largest) at the top of the bore, and similarly, the piston is coolest (and smallest) at the bottom of the bore when it is running in the engine. So this does make sense.
I have to admit that at 12,000 rpm, it is hard to imagine the piston changing diameter by 0.01mm in the 2.5 milliseconds it takes to travel from top to bottom of the cylinder. But hey, I am happy to run with this. :-)
For what it is worth, the Honda manual states that a piston to bore clearance of 0.035mm to 0.044mm with a service limit of 0.08mm. Piston OD is to be measured 15mm up from the bottom of the skirt on standard Honda pistons when working this out[/Edit]
So now, I can start to concentrate on the rest of the bike so that it is ready to take the engine.
Also, I soon hope to be receiving some brand new custom made MC18 conrods. Can't wait!
Progress on the custom made crankshaft has stalled out. STILL waiting on a quote! It's been about 3 months.
Actually, I did come across one other little point of interest. I found a parts list (in Japanese) for the MC21 online and downloaded it. It showed that the inner-most steel clutch plate had a different part number to the rest of the steel clutch plates. Also, the inner-most fibre clutch plate had a different part number than the rest of the fibre clutch plates.
I soon realised that one of my fibre clutch plates was indeed different to the rest as it had slots cut into four of the castellated engagement tabs to take anti-vibration rubbers. However, all 6 of the steel plates appeared to be similar. I double checked this on a spare MC18-SP engine that I have, and I found that one of the steel clutch plates was different. Most of the steel plates measure 2.89 - 2.94mm thick with my digital verniers. But there is a different steel plate that has a slightly concave shape that is made out of 2.0 mm thick steel. It measures about 3mm thick along the axis of the clutch due to its concave shape.
The different plates are the inner-most plates, The steel one sits so that the small diameter side of it goes on the inside. I went over the steel plates with some 240 grit wet-n-dry sandpaper just to "de-glaze" them a bit.
 |
| Progress,..... |
 |
| ......., at last |
I am currently trying to get some Wossner RM125 pistons. These are single ring pistons with about a 5mm shorter skirt than the standard NSR250 pistons. When/if I get them, I will be machining the heads slightly to get a good squish and even combustion volumes on both cylinders.
Well, my "A" barrels measured up to be 54.02mm diameter at the top and 54.01mm at the bottom.
So I will be getting pistons made to be 53.96mm max diameter so as to give 0.05mm clearance at the tightest diameter of the cylinder bore (being 54.01 the bottom at the bottom less 0.05mm)
Basically this is the 0.01 oversize 2000-2003 RM125 piston from Wossner. (Part Number 8061DB)
Wossner also do a NSR125 piston at 53.96. But I want to go nuts and get the (assumedly lighter) RM piston as it has a 5mm shorter skirt and a single ring.
.
[Edit] My man getting the Wossner pistons spoke to "Luigi" at Wossner in Germany. Luigi suggested going with a clearance of 0.05mm at the 54.02 diameter top of the bore. So the pistons will be 53.97mm nominal diameter. This change is very minor, but the piston is hottest (and largest) at the top of the bore, and similarly, the piston is coolest (and smallest) at the bottom of the bore when it is running in the engine. So this does make sense.
I have to admit that at 12,000 rpm, it is hard to imagine the piston changing diameter by 0.01mm in the 2.5 milliseconds it takes to travel from top to bottom of the cylinder. But hey, I am happy to run with this. :-)
For what it is worth, the Honda manual states that a piston to bore clearance of 0.035mm to 0.044mm with a service limit of 0.08mm. Piston OD is to be measured 15mm up from the bottom of the skirt on standard Honda pistons when working this out[/Edit]
So now, I can start to concentrate on the rest of the bike so that it is ready to take the engine.
Also, I soon hope to be receiving some brand new custom made MC18 conrods. Can't wait!
Progress on the custom made crankshaft has stalled out. STILL waiting on a quote! It's been about 3 months.
No comments:
Post a Comment